As disclosed in 3GPP TS 36.300, in an LTE (Long Term Evolution) mobile communication system, in order to realize mobility of a user while maintaining the communication quality of a mobile station (UE), the UE can be handed over from the original radio base station to a radio base station having a stronger received signal level.
When handover fails for some reason or when a problem occurs in the radio link during communication, communication can be recovered by carrying out reconnection control of the RRC (Radio Resource Control) connection between the UE and the radio base station.
In an LTE system, handover is arranged by the following procedures. First, a handover request is transmitted from the handover source radio base station (Source eNB) to the handover destination radio base station (Target eNB), and the Target eNB that has received the handover request judges whether the UE is able to obtain access based on access control rules such as service authorization and load. When it is determined that the UE is able to obtain access, the Target eNB then secures resources for the UE and returns to the Source eNB a signal indicating that the handover request will be accepted.
Handover is realized by means of the above-described arrangements. If handover fails for some reason, service can be continued by re-connecting the RRC connection and again attempting handover.
On the other hand, in order that reconnection control of the RRC connection may succeed, context information of the UE that includes a cell identifier that identifies the cell in which communication was realized up to this point, a UE identifier that uniquely identifies the UE in that cell, and an authentication code must be saved beforehand in the radio base station in which reconnection is performed. During the above-described handover preparation procedure, reconnection control can be implemented by transmitting the UE context information to the Target eNB.
In the above-described LTE system, techniques have been proposed for raising the success rate of handover or reconnection following handover failure.
For example, in Patent Document 1, the radio base station of the origin of movement selects a plurality of cells having good communication quality on the basis of communication quality reports of neighboring cells from the UE and implements a handover preparation procedure with respect to the plurality of radio base stations that manage these cells. The radio base station of the origin of movement then transmits information of the plurality of radio base stations that have completed the handover preparation to the UE.
The UE selects the movement destination cell that performs handover based on information of the radio base stations that have completed the handover preparation from the radio base station of the origin of movement and the communication quality of the neighboring cells at the time of receiving the information.
Literature of the Prior Art Patent Documents    Patent Document 1: WO2009/142054